Referring now to the drawings, wherein like features are designated by like reference numerals, FIG. 1 schematically illustrates one common type of prior-art, edge-emitting, separate-confinement-heterostructure, diode-laser 20 formed by epitaxially growing a series of semiconductor layers on an n-doped, semiconductor substrate 22. A lower electrical confinement or cladding region 24 of the diode-laser includes one or more n-doped semiconductor layers. Surmounting the lower cladding region is a lower optical confinement or waveguide region 26, formed by one or more undoped semiconductor layers. Surmounting the lower waveguide region is a so-called active region 28 including at least one undoped, active or quantum-well layer. If there is more than one quantum well layer, the quantum-well layers are separated by barrier layers (not shown). The active region is surmounted by an upper waveguide region 30, similar to lower waveguide region 24. Upper waveguide region 30 is surmounted in turn by an upper cladding region 32 including at least one p-doped semiconductor layer.
Typical Layer or Region Thickness
An elongated, rectangular electrode 34 is bonded to upper cladding region 32. Electrode 34 extends the entire length (L) of the diode-laser. The width W and length L of the electrode define the width of the diode-laser. The electrode and the region under the electrode are often referred to by practitioners of the art to as a “stripe”.
The diode-laser is energized (electrically pumped) by passing current through the layers between electrode 34 and substrate 22. Mirrors (not shown) on the ends (facets) of the laser form a laser resonant cavity. Energizing the laser generates electrical carriers that recombine in the active region to provide laser radiation that circulates in the resonant cavity. Laser radiation is emitted from the diode-laser in a general direction along a longitudinal (Z) axis of the laser. The radiation is emitted as a diverging beam (not shown) having a greater divergence in the Y-axis than in the X-axis. For this reason the Y-axis and X-axis are respectively referred to as the fast and slow axes by practitioners of the art.
Laser radiation circulating in the laser cavity is confined in the thickness (Y-axis) direction of the layers by reflection from interfaces between the waveguide regions and the cladding regions adjacent thereto. The circulating radiation is confined in the width (X-axis) direction, among other factors, by the width of the electrode, as it is only in this width that there is optical gain.
This type of diode-laser typically has a stripe-length between about 1.0 and 1.5 millimeters (mm), and emits radiation from an emitting aperture having a height H of about 1.0 micrometer (μm) and a width W between about 4.0 and 200 μm. The emitting aperture height H includes the combined thickness of the upper and lower waveguide regions 30 and 26 and the active region 28. Width W is usually referred to in the art as the emitter-width or stripe-width. A diode-laser having an emitter-width greater than about 30 μm is often referred to as a wide-emitter diode-laser.
Generally, for a given length of a diode-laser, the greater the stripe (emitter) width, the greater will be the potential output power of the diode-laser. However, the wider the stripe width, the greater is the number of transverse modes at which the laser delivers output radiation. The greater the number of transverse modes, the poorer is the quality of the output beam of the diode-laser. While a multiple transverse mode output beam is acceptable for diode-laser applications such a heating and surface treatment, it is often not suitable for applications in which the output beam must be focused into a small spot, for example in end-pumping a fiber laser. There is a need for a wide-stripe diode-laser that operates in a single transverse mode.